Plenty of Room at the Bottom?

By focusing on evolutionary increases in brain size, biologists generally have overlooked nervous system organization in the smallest of animals. But when one looks closely at very small animals, an important question emerges: Where can a relatively large brain fit in a small body? The answers displayed by one animal after another deliver a new perspective on variation in nervous system design among animals. And this variation calls into question some basic assumptions regarding the uniformity of how central nervous systems function overall. In other words, much remains to be learned from the smallest of the small.